With regard to a grounding structure for a circuit board, for example, various structures are conventionally known as a method for connecting an earth of a printed circuit board, for example. For example, as depicted in FIG. 5, a connection lead wire 707 is attached from an earth potential (reference potential terminal) of a printed circuit board 2, and a round (annular) crimped terminal (solderless ring-type terminal) 701 is attached to a tip of the connection lead wire 707 and is connected to an earth member 3 by a screw 4 in a known structure.
However, in such a conventional method for attaching the round crimped terminal 701, the screw 4 may obliquely be driven relative to the crimped terminal 701 and the earth member 3 or the screw may incompletely be fastened due to an insufficient torque force. In such a case, the earth connection (i.e., “grounding”) of the printed circuit board 2 may be incomplete.
If the earth connection is incomplete, an electric shock may occur in devices and apparatuses incorporating a printed circuit board. For example, if a printed circuit board is used in a high voltage circuit for a magnetron in a microwave oven that is a microwave heating apparatus and the earth connection of the high voltage circuit is incomplete, an electric discharge may occur between an earth member and a screw or an electric shock may even occur in the case of an electric discharge toward the primary side.
To improve such incomplete earth connection of a printed circuit board, a configuration is proposed that has a connection member 101 attached to the printed circuit board 2 and connected to the earth member 3 by the screw 4 as depicted in FIGS. 6a, 6b (see, e.g., Patent Document 1).
FIG. 6a is a plane view of a connection member of Patent Document 1 viewed from a component mounting surface and FIG. 6b is a cross-sectional view taken along a portion A-A′ of FIG. 6a viewed in the direction of arrows.
As depicted in FIGS. 6a and 6b, the grounding structure of Patent Document 1 has the plate-shaped connection member 101 disposed on an upper surface of the printed circuit board 2 such that the connection member 101 is connected to a reference potential terminal 7 of the printed circuit board 2 while the connection member 101 and the printed circuit board 2 are fixed to the earth member 3 (e.g., an earth metal part) by using the screw 4. Protruding portions 101a and 101b protruding toward a back surface of the printed circuit board 2 are formed at respective end portions of the connection member 101, and these two protruding portions are inserted in holes of the printed circuit board 2 to position the connection member 101 relative to the printed circuit board 2. The one protruding portion 101a of the connection member 101 is electrically connected through a solder 5 to the reference potential terminal 7 of the printed circuit board 2. A circular through-hole 101c for allowing penetration of the screw 4A is formed in a center portion of the connection member 101, and a through-hole is also formed in the printed circuit board 2. The earth member 3 is fixed to a bracket 6, for example.
Since the plate-shaped connection member 101 can certainly be positioned relative to the printed circuit board 2 by using the two protruding portions 101a, 101b disposed on the connection member 101 in the grounding structure of Patent Document 1 as described above, the connection member 101 does not rotate during fastening by the screw 4 and the screw fastening can certainly be performed to achieve safe earth connection.
Patent Document 1: JP H1-235171 A